The Harlequins winger was banned for a year and the club fined £215,000 – 50% suspended – after being found to have fabricated a cut to the mouth in last season’s Heineken Cup quarter-final against Leinster.

Hopley questioned how Williams could deserve a one-year ban given Schalk Burger received an eight-week suspension for eye-gouging and Justin Harrison got eight months for admitting three drug-related charges.

“In recent weeks we have seen players found guilty of eye-gouging receiving bans of between eight and 12 weeks, and another player found guilty of misconduct receive an eight-month ban,” said Hopley, Professional Rugby Players’ Association chief executive.

“For Tom Williams to be singled out and handed a 12-month ban is both excessive and entirely disproportionate. It is an extraordinary decision.”

Williams was found to have faked a cut to his mouth which allowed Harlequins to send specialist goal-kicker Nick Evans, previously substituted, back onto the field with five minutes remaining and Leinster leading 6-5.

Harlequins had a late drop-goal attempt but Evans, struggling with a knee injury, pulled it wide and Leinster won the game.